Plate TectonicsCharlotte CarterEarth Science

Unit Review

Drifting Continent

s• Evidence of drifting– Fossils found on both of the

continents of Africa and South America that are of the same organism

• Fossils: The preserved remains of ancient organisms

– German scientist Alfred Wegner came up with the theory of continental drift, he was actually a meteorologist and not a geologist

• The theory called the giant landmass that once was on Earth Pangaea

– Pangaea: Means all Earth•Early Earth & Plate Tectonics

Fossil Evidenc

e• Fossils play a key role in

supporting the theory of Continental drift– Glossopteris is an extinct

plant• They are found in rocks that

are around 250,000,000 years old ( 250 million)

• The seeds were to large to be carried by wind and too fragile to have survived ocean waves

• The fact that they are found in Antarctica implies that they had to be in a better climate than what is present Antarctica

Fossils• Glossopteris: a fern found on the

southern continents

• Cynognathus: a land reptile found in South America and Africa

• Lystrosaurus: a land reptile found in Africa, Antarctica, and India

• Mesosaurus: a freshwater swimming reptile found in Africa and South America

Geologic Evidenc

e• From Rocks– Not only fossils provide

evidence for theory support• Rocks in Africa and South

America– When you examine the

continents of Africa and South America,they look as if they could piece together like a puzzle

– The layers of coal depth line up with each other

– Rock deposits from glaciers also match

Naval oceanography made two significant contributions in the advancement of the theory of

plate tectonics.

• .1. The charting of the ocean floor using echo sounding refined the

understanding of seafloor structure 2. Studies of the sea floor using instruments called magnetometers

revealed strong evidence in support of seafloor spreading.

• Just as maps of the oceans and coastlines initiated the idea of continental drift, maps of the ocean floor propelled science into the investigation of seafloor spreading. Charts and studies of the mid ocean ridge system, trenches, seamounts, and continental shelves—have been examined and catalogued.

• Using these and other data, Harry Hess and Charles Dietz proposed the idea of seafloor spreading. They suggested that the worldwide system of undersea mountains called the mid-ocean ridges is where new ocean floor is created as plates move apart. As they diverge, they move large crustal plates along with the continents that sit atop of them.

Divergent Boundary

• Divergent Boundaries

– Constructive-add new land

– Mid-ocean Ridge• Ocean floor moves away

on either side of the ridge• Called sea-floor spreading• Often offset by transform

faults which causes a curve in the ridge

Transform Faults

Sea-Floor Spreading/Mid-Ocean Ridge

Spreading Sea Floor

Basic Plate Boundaries

Magnetic Rock Strips

•Some minerals (such as magnetite) have magnetic properties

•These minerals line up with the Earth’s magnetic poles

•When the molten rock hardens, a permanent record of the Earth’s magnetism remains

•The Earth’s magnetic poles have reversed themselves from time to time

•Animation

•Sea Floor Spreading

Convergent Boundaries

• Plates collide-destructive• Two continents colliding

build mountains or plateaus

• The Indian Plate and the Eurasian Plate collide to form the Himalayas which have Mt. Everest , the highest mountain on Earth.

Convergent Boundary • Destructive-crust is

destroyed (melted by the mantle)

• Called Subduction• When oceanic and

continental crust collide • Oceanic crust is pushed

down into the mantle and melted

• Some of this melted material surges upward

• The continental crust is also forced upward producing volcanoes

• The Cascade Range in Washington and Oregon are an example of this

Convergent Boundaries

Convergent Boundaries

Convergent

Boundaries• When two oceanic

plates collide subduction occurs

• The older denser plate is pushed into the mantle and melted

• Some of the material rises upward and erupts on the ocean floor forming an island arc

Theory of Plate

Tectonics• Tectonics: refers to the branch of geology that is concerned with plate movements

• Theory of Plate Tectonics: Links together the ideas of continental drift and ocean floor spreading to explain how the Earth has evolved over time.– It explains the formation, movements, collisions, and

destruction of the Earth’s crust– According to the theory the Earth’s uppermost layer, called

the lithosphere, is made up of plates

Lithospheric Plates• There are seven major plates

– The Pacific Plate- • which covers 1/5 of the Earth

– North American– South American– Eurasian– African– Indo-Australian– Antarctic Plates

• There are also Many smaller plates– Caribbean– Arabian

• Plate Tectonics Review

SUMMATION

• The theory of plate tectonics is relatively new• Early 1900s, Alfred Wegener first developed a theory of

continental drift based on a collection of evidence from rocks and fossils found on continents separated by vast distances

• 1928, Arthur Holmes proposed a mechanism to explain how the continents could have moved across Earth's surface

• Circular convection currents of molten material deep within Earth could provide ample force to divide and move continents

• By the late 1960s, evidence of seafloor spreading helped to support the now well-accepted theory of plate tectonics.